This invention relates generally to liquid handling devices, and more particularly to improvements therein for loading of liquid.
Liquid handling devices of various specific types are presently used in many forms and applications. An usual basic structure found in such devices is a piston chamber and a piston which, when reciprocated, either draws fluid into the piston chamber or discharges it therefrom. Many such instruments are small and hand-held, and have attached thereto a needle or some other liquid receptacle through which liquid is drawn and discharged upon operation of the piston. The loading of liquid into the piston chamber of such devices presently results in air being drawn in as well since the piston is not immediately in contact with the liquid being loaded. An air space exists within the piston chamber and between the piston and the liquid to be loaded. This air remains after the desired liquid is drawn into the device.
In liquid transfer or dispensing device, such as the type used most frequently in chemical and medical laboratories, this air has to be taken into account in designing the device since the air trapped therein is compressible. This air thus affects the amount of liquid dispensed upon a given movement of the piston. Although the air interface is of no concern for many applications, it is desirable for precision applications that the air be eliminated before use.
Another commonly used liquid dispensing device is a medical syringe for inoculating animals and humans. Air must be eliminated from such a device prior to inoculation. The air is presently eliminated after filling by turning the syringe with its needle extending upright and displacing volume within the piston chamber until all of the air is expelled. This is awkward and requires a separate air purging manipulation.
It is, therefore, a principal object of the present invention to provide an improved technique and structure for purging air from liquid handling devices before use.